Summary After a training flight, the pilot owner, accompanied by his instructor, landed the Piper PA-23 at the Saint-Mathias aerodrome, Quebec, to refuel. After refuelling, which took approximately 30 minutes, the pilot taxied the aircraft for a flight to the Beloeil airport, Quebec. Prior to take-off, the pilot did a run-up of about five minutes. During the initial climb, shortly after take-off, at a height of about three feet above ground level, the instructor, who was sitting in the right-hand seat, observed smoke emanating from the rear of the right engine. He told the pilot to land the aircraft immediately. The pilot landed the aircraft on the runway ahead, and the aircraft came to a stop in a ditch located at the end of the runway. The two occupants evacuated the aircraft quickly and without any difficulty. Shortly thereafter, the local firefighters arrived and extinguished the fire that had broken out under the aircraft's right nacelle, where fuel was running onto the ground. No one was injured. Ce rapport est galemement disponible en franais. Other Factual Information The crew was certified and qualified for the flight according to existing regulations. The gravel runway measured 2,000 feet long by 50 feet wide. The aircraft landed with the landing gear down and locked. The fuel selector was in the Main position during take-off and during the inspection of the aircraft. Examination of the aircraft confirmed that the source of the fire was under the right nacelle in the area occupied by the fuel supply selector for the right engine, the fuel filter, and the auxiliary fuel pump. The damage caused by the fire ran from the right engine, near the firewall, towards the back of the firewall. The spar had been completely destroyed by the fire and no longer supported the wing. Examination of the electrical system did not reveal any sign of a short circuit. No circuit breaker had disconnected from the electrical system. A single line in the hydraulic system was ruptured. The line was not actuated during the take-off run and was not in an area where a fire could have started in the event of a leak of hydraulic fluid. The fire consumed the fuel filter and its adjacent parts as well as the fuel lines for selecting the tanks. The fuel system was at the centre of the source of the fire. The auxiliary pump, also located in this area, fell off onto the ground during the fire. This pump is normally supposed to be fastened to the structure by two bolts and nuts, but only one retaining bolt was in place. The other retaining point did not show any trace of a bolt having been present before the fire. Further, the fitting that connected the fuel supply to the pump was not fully tightened, and fuel could leak out. The fuel filter was supposed to be fastened to the pump fitting, but no trace of the filter was found. The retaining points of the auxiliary fuel pump did not show any sign of electrical arcing. The aircraft was certified and maintained in accordance with existing regulations and approved procedures. It was not fitted with a fire indicator, nor is one required for this type of aircraft.